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  <div class="question_difficulty">
   难度：Medium
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   <h1 class="question_title">
    652. Find Duplicate Subtrees
   </h1>
   <p>
    Given a binary tree, return all duplicate subtrees. For each kind of duplicate subtrees, you only need to return the root node of any
    <b>
     one
    </b>
    of them.
   </p>
   <p>
    Two trees are duplicate if they have the same structure with same node values.
   </p>
   <p>
    <b>
     Example 1:
    </b>
   </p>
   <pre>
        1
       / \
      2   3
     /   / \
    4   2   4
       /
      4
</pre>
   <p>
    The following are two duplicate subtrees:
   </p>
   <pre>
      2
     /
    4
</pre>
   <p>
    and
   </p>
   <pre>
    4
</pre>
   Therefore, you need to return above trees' root in the form of a list.
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   <h1 class="question_title">
    652. 寻找重复的子树
   </h1>
   <p>
    给定一棵二叉树，返回所有重复的子树。对于同一类的重复子树，你只需要返回其中任意
    <strong>
     一棵
    </strong>
    的根结点即可。
   </p>
   <p>
    两棵树重复是指它们具有相同的结构以及相同的结点值。
   </p>
   <p>
    <strong>
     示例 1：
    </strong>
   </p>
   <pre>        1
       / \
      2   3
     /   / \
    4   2   4
       /
      4
</pre>
   <p>
    下面是两个重复的子树：
   </p>
   <pre>      2
     /
    4
</pre>
   <p>
    和
   </p>
   <pre>    4
</pre>
   <p>
    因此，你需要以列表的形式返回上述重复子树的根结点。
   </p>
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